When she was 8, Ruth Wilson liked re-enacting movie scenes with her two rambunctious brothers. One of her favorites, she recalled the other day, was the ending of “Platoon,” in which Willem Dafoe, peppered by bullets, collapses in slow motion on a verdant field.

Some time ago, Jimmy Fallon urged Ms. Wilson to replay that sequence for his late-night audience. She was game, kicking off her pumps, stepping to center stage in a sexy little cocktail dress, taking one imaginary bullet after another, and writhing theatrically before sinking to the floor.

There was something feline in her performance. But then, as she would tell you, she was doing what comes naturally. There is no obvious slink in her gait, no purr in her voice, though in an interview she extended a leg elastically to show off her pale Chanel sandals. In Manhattan last week to talk up “The Little Stranger,” the new gothic thriller that opens on Aug. 31, she confessed to feeling a kind of eerie kinship with cats.

“A cat is incredibly physical, and as a performer I’m physical,” she said. “If I feel emotions, they move through my body in a way that is sensual. I’m not necessarily in control of that.”

She decided to explore that feral energy during a visit to Koneko, a cat cafe on the Lower East Side, an oddball setting for an interview, as she noted wryly.

“But I thought, Why not? We don’t have these sorts of places where I’m from in England, so I wanted to see what this is about.”

Her affinity for the creatures scrambling in and out of boxes in the gymlike space at the rear of the cafe is more than physical. As emotionally agile as the characters she plays, Ms. Wilson can seem simultaneously self-contained and playful, inquisitive yet somehow disengaged, her core, if such a thing can be isolated, always tantalizingly out of reach.

Even the source of her beauty is hard to pin down, her features rendered slightly off-kilter by a distractingly wide mouth and swollen upper lip.

Her elusiveness, along with a subterranean sensuality, has made her a force field, her often-troubled characters magnetizing filmmakers and audiences alike. She is Alice, Idris Elba’s nemesis, a disarmingly seductive serial killer in the television series “Luther.” She played opposite Jake Gyllenhaal in a Broadway production of “Constellations,” about two lovers caused by the laws of physics to meet over and over again.

Ms. Wilson, 36, is perhaps best known to Americans as Alison, the alternately spirited and brooding temptress of “The Affair,” which wrapped its fourth season, her last, on Showtime this month. (More about that later.)

Leaving the show was apparently not much of a setback. Directors have vied to cast her for a string of roles that in the last year alone have included “His Dark Materials,” a television adaptation of Philip Pullman’s metaphysically tinged children’s trilogy, and another as a Yorkshire sheep farmer in the film “Dark River.”

She has also produced and is starring in “Mrs. Wilson,” as her own grandmother, who in the 1960s, after the death of her husband, an MI6 agent, discovered that he had been living intermittently with three other wives.

The fashion world, too, has begun to fetishize Ms. Wilson, documenting her red carpet pivots dressed in a succession of high-glam labels, including Oscar de la Renta, Prada and Christian Dior. But it is the suggestion of an overpowering inner life that mostly gets under the skin.

“I’m a tragedienne in some way,” Ms. Wilson said between measured sips of a cappuccino. Its frothy surface, kitschily embellished with a tiny cat face, made her laugh but otherwise failed to distract. “I think quite epically,” she went on. “I like epic landscapes and grand emotions.”

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Ms. Wilson as Alison plays siren to Dominic West as Noah in “The Affair.”CreditShowtime

Outsize feelings roiled beneath Alison’s surface in “The Affair,” Ms. Wilson’s unsettling performance having earned her a 2015 Golden Globe for best actress in a television series. This season, the fourth and penultimate, her character is killed.

Her abrupt demise may have struck some viewers as a haunting inevitability. Others were crushed, venting on Twitter. “How could she be written out like this?” @lostshayid lamented. “I wanted to see her happy with or without Cole/Noah in the end.”

And Jamie@ImposingLaird tweeted sourly: “Her character deserved so much better. So disappointed.”

Ms. Wilson would not explain why she is leaving the show, though it has been widely suggested that her termination was punishment for having complained that she had been paid less than Dominic West, a male lead on the show. Others ventured that she had simply found a better role.

“It isn’t about pay parity, and it wasn’t about other jobs,” Ms. Wilson said. She added coolly, “But I’m not really allowed to talk about it.”

There was a meaningful silence. “There is a much bigger story,” she eventually volunteered, urging me, more than once, to contact Sarah Treem, a writer and producer of the show.

Ms. Treem did not amplify, repeating in an email a statement previously issued by Showtime. “The character of Allison had run its course,” she wrote. “By completing her arc this season, the consequences of her death will lead to compelling story lines for our final season.”

As Caroline in “The Little Stranger,” adapted from Sarah Water’s post-World War I ghost story, Ms. Wilson’s unraveling is more subtle, her steaminess less overt. She had tamped down her looks for the role, bulking up her slender frame with padding, hiding her curves inside a series of drab country frocks.

“My teeth were made to stick out,” she said. “I had a weird walk. I think there was a sense of Caroline as definitely not the pretty girl.”

Not man averse, though. “I asked Sarah: ‘What’s Caroline’s sexuality? Is she a lesbian?’ I wasn’t sure. But she told me, ‘No, I never wrote her that way.’”

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At Koneko, in the cat gym. CreditAn Rong Xu for The New York Times

Even as the mistress of a country manor, Ms. Wilson is sexy in a way that disturbed her as a girl. “I remember being about 14 when I started wearing shorts and heels,” she recalled. “I hated the attention I got. I found it overwhelming.” She deflected unwelcome stares and catcalls, she said, by going undercover in jeans and her brothers’ rugby shirts.

“I don’t know if I’m different in this way from other women,” she said. “Lots of us are aware of the power of our sexuality, but we don’t always know how to control it.”

In the past she has felt pressured to flash her breasts on screen while her male counterparts, for the most part, got to keep their privates under wraps. She has grumbled publicly about the Hollywood tendency not just to expose acres of flesh but to probe female sexuality in ways she finds more than a little unbalanced.

“Why have I always got to do the orgasm face,” she once chided. “There should be a male orgasm face.”

But she wasn’t here to take on the industry. Growing a little restive, she made her way toward the glass enclosure housing the cafe cats. Once inside, she began coaxing them out of their hidey-holes, fondling and teasing them.

“Cats don’t need you that much,” Ms. Wilson said. “They like to come and get stroked now and then, and they need you to feed them. But other than that, they’re not very demanding, are they? I quite like that.”